The Irish Government should come clean on its own past "failures" after a report uncovered police collusion with the IRA, Democratic Unionists said.
Paul Givan claimed the Dublin administration helped create the republican armed group years before events examined by a judge in Ireland during a critical probe into the Irish police force's actions.
Judge Peter Smithwick found that an IRA mole in the Garda station in Dundalk tipped off a terrorist hit squad that led to the murders of two of the most senior Royal Ulster Constabulary (RUC) men killed during the Troubles - Chief Superintendent Harry Breen and Superintendent Bob Buchanan.
They were ambushed by Provo killers on a back road on their way home to Northern Ireland after meeting Garda officers in the border town on March 20, 1989.
DUP Stormont MLA Paul Givan said: "The fact that the political establishment in Dublin is shocked by the revelations I find shocking, any process (for dealing with past wrongdoing) must also look at the actions of the Irish Government."
He accused the Republic's government of assisting in the creation of the IRA. Former prime minister Charles Haughey and three others were cleared in 1970 of illegally importing arms for the IRA's use in Northern Ireland.
"This report should be the catalyst that brings forward the truth about the failings of the Irish Government and its agencies but ultimate responsibility lies with the Provisional IRA that carried out the cold-blooded murder of Harry Breen and Bob Buchanan and wreaked havoc for decades," Mr Givan added.
Garda Commissioner Martin Callinan, who leads the force, has said he is horrified that Smithwick found that a terrorist mole in the ranks of the force gave the IRA a tip-off and accepted the tribunal's conclusions. But he said he would never accept that officers valued loyalty to the force over the truth.
Irish Justice Minister Alan Shatter has apologised "without reservation" to the families of the RUC officers for any failings on the part of the state that were identified in the Smithwick report.
Sinn Fein MLA Gerry Kelly told the DUP during a Stormont debate: "They need to realise that if it is the truth that they are looking (for) then let it come on the basis of equality, on the basis of parity of esteem, on the basis of mutual respect.
"Let's get away from the hierarchy of victims, let's realise that, as an example, Pat Finucane's (murdered by loyalists) family deserves your support as well as everybody else's."
Stormont justice minister David Ford said the speedy response by the Taoiseach, the Tanaiste and Mr Shatter, in particular the absolute and unqualified apology for any failings of the Irish state or its agencies, was welcomed.
"Looking forward, I know the Garda Commissioner is considering if new lines of inquiry arise in respect of the murders," he added.
Three recommendations in the report relate to relations between Northern Ireland and the Republic.
Mr Ford said: "Let me say first that I remain committed to strengthening north/south co-operation wherever possible and building on the progress we have already made."